[fmax30]

I don't think that this is such a good idea, as mentioned above by others, during peak hours the trains are almost over capacity (At least in Munich where I currently live). Making them free would lead to a degraded experience for everyone.

One of the major reasons that I am not in favor is because in Pakistan ( where I am originally from) they launched a Metro Bus service a few years ago, the fare was a nominal flat rate ( ~ 15 euro-cents) for traveling as much as you can in one direction. Now although it is a great service for the people but the buses are always over crowded, and because they are incurring a loss and the government has to spend millions of dollars per year in subsidies just to keep it afloat; They have not upgraded capacity and it is really inconvenient to travel on those buses ( I remember getting sick 4-5 times a year when I regularly traveled on those buses).

A better solution would to be start banning the diesel engine, ramp up the taxes for fossil fuel based cars. And to force factories to reduce their carbon emissions.

[vidarh]

It will only lead to overcrowding if the service is still good enough that more people than today find it worthwhile to deal with.